Saudi King Abdullah appeared on state television on Wednesday for the first time since he underwent a back operation on 18 November.

The 89-year-old monarch was shown seated and receiving well-wishers at the King Abdul Aziz Medical City for the National Guard in the capital Riyadh.

The footage came as rumours were awash that the health of the leader of the world's key oil producer had taken a sharp turn for the worse.

"He thanked all those who have wished him well," state news agency SPA reported.

On Monday, Crown Prince Salman assured cabinet members over the health of the king, state news agency SPA reported.

Abdullah had undergone a new operation to correct "a ligamentary slackening in the upper back."

State media had reported daily on the stream of family members going to check on the king's health over the past 11 days. However, until Wednesday, all visitors had been received by his eldest son Mitaab.

The king's absence from the public gaze had sparked growing rumours about his health on social networking website Twitter.

The king had a similar operation in October 2011. In November 2010, he was operated on in New York for a slipped disc complicated by a blood clot that put pressure on his spine, and he underwent a further operation the following month before convalescing for a month in Morocco.

The king's age and frequent hospitalisations have raised concerns about the future leadership of the world's key oil producer.

The heir to the throne is his half-brother Crown Prince Salman, 76, who was named to the succession on the death of Prince Nayef in June.